For millions of years, L1 retrotransposons have been duplicating in mammalian genomes by an efficient "copy and paste" mechanism; consequently, L1s now make up 15% of the human genome. These autonomous elements are thought to have played an important role in the expansion and evolution of our genome. For example, a recent, and still active, L1 element was found to have inserted into genes, thereby causing disease. We will show examples of 3' transduction events for this particular L1, which represents another mechanism by which L1s have probably shaped the human genome. Part of the preparation for this project involves a complete analysis of the L1 elements in the human genome sequence has been performed. Of particular interest has been the development of an improved algorithm for the identification of the target-site duplications that flank the L1 insertion sequences.